Chronic kidney disease (CKD) is a public health epidemic that increases risk of death due to cardiovascular disease. Left ventricular hypertrophy (LVH) is an important mechanism of cardiovascular disease in individuals with CKD. Elevated levels of FGF23 have been linked to greater risks of LVH and mortality in patients with CKD, but whether these risks represent causal effects of FGF23 is unknown. Here, we report that elevated FGF23 levels are independently associated with LVH in a large, racially diverse CKD cohort. FGF23 caused pathological hypertrophy of isolated rat cardiomyocytes via FGF receptor-dependent activation of the calcineurin-NFAT signaling pathway, but this effect was independent of klotho, the coreceptor for FGF23 in the kidney and parathyroid glands. Intramyocardial or intravenous injection of FGF23 in wild-type mice resulted in LVH, and klotho-deficient mice demonstrated elevated FGF23 levels and LVH. In an established animal model of CKD, treatment with an FGF-receptor blocker attenuated LVH, although no change in blood pressure was observed. These results unveil a klotho-independent, causal role for FGF23 in the pathogenesis of LVH and suggest that chronically elevated FGF23 levels contribute directly to high rates of LVH and mortality in individuals with CKD.

Rationale The regenerative potential of the heart is insufficient to fully restore functioning myocardium after injury, motivating the quest for a cell-based replacement strategy. Bone marrow derived mesenchymal stem cells (MSC) have the capacity for cardiac repair that appears to exceed their capacity for differentiation into cardiac myocytes. Objective Here we test the hypothesis that bone marrow derived MSCs stimulate the proliferation and differentiation of endogenous cardiac stem cells (CSCs) as part of their regenerative repertoire. Methods And Results Female Yorkshire pigs (n=31) underwent experimental myocardial Infarction (MI); and 3 days later received transendocardial injections of allogeneic male bone marrow-derived MSCs, MSC concentrated conditioned medium (CCM), or placebo (Plasmalyte). A no-injection control group was also studied. MSCs engrafted and differentiated into cardiomyocytes and vascular structures. In addition, endogenous c-kit+ CSCs increased 20-fold in MSC treated animals vs. controls (p<0.001), there was a 6-fold increase in GATA-4+ CSCs in MSC vs. control (p<0.001), and mitotic myocytes increased 4-fold. Porcine endomyocardial biopsies were harvested and plated as organotypic cultures in the presence or absence of MSC feeder layers. In vitro, MSCs stimulated c-kit+ CSCs proliferation into enriched populations of adult cardioblasts that expressed Nkx2-5 and troponin I. Conclusions MSCs stimulate host CSCs, a new mechanism of action underlying successful cell-based therapeutics.

The mechanism(s) underlying cardiac reparative effects of bone marrow-derived mesenchymal stem cells (MSC) remain highly controversial. Here we tested the hypothesis that MSCs regenerate chronically infarcted myocardium through mechanisms comprising long-term engraftment and trilineage differentiation. Twelve weeks after myocardial infarction, female swine received catheterbased transendocardial injections of either placebo (n ‫؍‬ 4) or male allogeneic MSCs (200 million; n ‫؍‬ 6). Animals underwent serial cardiac magnetic resonance imaging, and in vivo cell fate was determined by co-localization of Y-chromosome (Y pos ) cells with markers of cardiac, vascular muscle, and endothelial lineages. MSCs engrafted in infarct and border zones and differentiated into cardiomyocytes as ascertained by co-localization with GATA-4, Nkx2.5, and ␣-sarcomeric actin. In addition, Y pos MSCs exhibited vascular smooth muscle and endothelial cell differentiation, contributing to large and small vessel formation. Infarct size was reduced from 19.3 ؎ 1.7% to 13.9 ؎ 2.0% (P < 0.001), and ejection fraction (EF) increased from 35.0 ؎ 1.7% to 41.3 ؎ 2.7% (P < 0.05) in MSC but not placebo pigs over 12 weeks. This was accompanied by increases in regional contractility and myocardial blood flow (MBF), particularly in the infarct border zone. Importantly, MSC engraftment correlated with functional recovery in contractility (R ‫؍‬ 0.85, P < 0.05) and MBF (R ‫؍‬ 0.76, P < 0.01). Together these findings demonstrate long-term MSC survival, engraftment, and trilineage differentiation following transplantation into chronically scarred myocardium. MSCs are an adult stem cell with the capacity for cardiomyogenesis and vasculogenesis which contribute, at least in part, to their ability to repair chronically scarred myocardium.cardiac chimerism ͉ cellular cardiomyoplasty ͉ heart failure ͉ catheter delivery

To demonstrate the safety of transendocardial stem cell injection (TESI) with autologous MSCs and BMCs in patients with ICM.• To assess prespecified outcomes of efficacy.

With serially obtained MRI and MDCT, we demonstrate in vivo reappearance of myocardial tissue in the MI zone accompanied by time-dependent restoration of contractile function. These data are consistent with a regenerative process, highlight the value of noninvasive multimodality imaging to assess the structural and functional basis for myocardial regenerative strategies, and have potential clinical applications.

The underlying mechanism(s) of improved left ventricular function (LV) due to mesenchymal stem cell (MSC) administration after myocardial infarction (MI) remains highly controversial. Myocardial regeneration and neovascularization, which leads to increased tissue perfusion, are proposed mechanisms. Here we demonstrate that delivery of MSCs 3 days after MI increased tissue perfusion in a manner that preceded improved LV function in a porcine model. MI was induced in pigs by 60-min occlusion of the left anterior descending coronary artery, followed by reperfusion. Pigs were assigned to receive intramyocardial injection of allogeneic MSCs (200 million, approximately 15 injections) (n = 10), placebo (n = 6), or no intervention (n = 8). Resting myocardial blood flow (MBF) was serially assessed by first-pass perfusion magnetic resonance imaging (MRI) over an 8-wk period. Over the first week, resting MBF in the infarct area of MSC-treated pigs increased compared with placebo-injected and untreated animals [0.17 +/- 0.03, 0.09 +/- 0.01, and 0.08 +/- 0.01, respectively, signal intensity ratio of MI to left ventricular blood pool (LVBP); P < 0.01 vs. placebo, P < 0.01 vs. nontreated]. In contrast, the signal intensity ratios of the three groups were indistinguishable at weeks 4 and 8. However, MSC-treated animals showed larger, more mature vessels and less apoptosis in the infarct zones and improved regional and global LV function at week 8. Together these findings suggest that an early increase in tissue perfusion precedes improvements in LV function and a reduction in apoptosis in MSC-treated hearts. Cardiac MRI-based measures of blood flow may be a useful tool to predict a successful myocardial regenerative process after MSC treatment.

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Rationale Cardiac myocyte hypertrophy is the main compensatory response to chronic stress on the heart. p90 Ribosomal S6 Kinase (RSK) family members are effectors for extracellular signal-regulated kinases that induce myocyte growth. Although increased RSK activity has been observed in stressed myocytes, the functions of individual RSK family members have remained poorly defined, despite being potential therapeutic targets for cardiac disease. Objective To demonstrate that type 3 RSK (RSK3) is required for cardiac myocyte hypertrophy. Methods and Results RSK3 contains a unique N-terminal domain that is not conserved in other RSK family members. We show that this domain mediates the regulated binding of RSK3 to the muscle A-kinase anchoring protein (mAKAP) scaffold, defining a novel kinase anchoring event. Disruption of both RSK3 expression using RNA interference and RSK3 anchoring using a competing mAKAP peptide inhibited the hypertrophy of cultured myocytes. In vivo, RSK3 gene deletion in the mouse attenuated the concentric myocyte hypertrophy induced by pressure overload and catecholamine infusion. Conclusions Taken together, these data demonstrate that anchored RSK3 transduces signals that modulate pathologic myocyte growth. Targeting of signaling complexes that contain select kinase isoforms should provide an approach for the specific inhibition of cardiac myocyte hypertrophy and for the development of novel strategies for the prevention and treatment of heart failure.